<!DOCTYPE HTML>
<html>

<head>
  <meta charset="utf-8">
  <style>
    .menu ul {
      margin: 0;
      list-style: none;
      padding-left: 20px;
      display: none;
    }

    .menu .title {
      font-size: 18px;
      cursor: pointer;
    }

    .menu .title::before {
      content: '▶ ';
      font-size: 80%;
      color: green;
    }

    .menu.open .title::before {
      content: '▼ ';
    }

    .menu.open ul {
      display: block;
    }
  </style>
</head>

<body>

  <div id="sweeties" class="menu">
    <span class="title">Sweeties (click me)!</span>
    <ul>
      <li>Cake</li>
      <li>Donut</li>
      <li>Honey</li>
    </ul>

  </div>

  <script>
    let menuElem = document.getElementById('sweeties');
    let titleElem = menuElem.querySelector('.title');

    titleElem.onclick = function() {
      menuElem.classList.toggle('open');
    };
  </script>

</body>
</html>
